1. Field of the Invention
This invention relates to a polyethylene terephthalate film for use as a support of photographic film and, more particularly, to a polyethylene terephthalate film for use as a support of radiographic film.
2. Description of the Prior Art
It is desirable for radiographic films to be colored blue or bluish purple to facilitate the viewing of a photographic image thereon. It is also desirable for radiographic film supports to have a minimal absorption in the short wavelength region, because the radiograph film is sensitive to radiations of short wavelength. Therefore, to the degree that the support absorbs such radiations desensitization results by the filtering action of the support on the photo-sensitive emulsion layer. That is, ordinary radiographic film consists of a support bearing a photo-sensitive emulsion on the both surfaces thereof and image cntrast is reduced by a support possessing a yellow tint.
It is, accordingly, desirable to color the support material, e.g., a polyethylene terephthalate, of such films a blue or bluish-purple color to avoid the presence of such a yellow tint.
The coloring matter to use for coloring a polyethylene terephthalate film, for use as the support layer of a radiographic film, blue or bluish-purple should be such that it has good thermal resistance, good compatibility with polyethylene terephthalate and proper chromaticity. Also, it should be inert to the silver halide emulsion; that is, it should have no adverse effect on photographic characteristics, such as sensitivity, gamma and fog.
Since the manufacture of polyethylene terephthalate film on a commercial scale is by a hot melt extrusion process, coloring material to be incorporated therein is required to have high thermal resistance, withstanding temperatures of from 270.degree. to 300.degree.C. It is difficult to manufacture a colored or pigmented polyethylene terephthalate film by dyeing or like coloring treatment of an unpigmented film due to its very stable physical structure. Therefore, a mass coloring process is preferred, in which a coloring material is dissolved or dispersed in the polyethylene terephthalate during the synthesis or hot melt processing thereof. Accordingly, the coloring material is required to have high thermal resistance, withstanding processing temperatures of 270.degree. to 300.degree.C without any decomposition and discoloration. Use of a mass coloring process has the advantage that pigmentation is attained concurrently with the molding process and does not require any other step.
In such mass coloring, it is required that the coloring material be easily and uniformly dispersed or dissolved in the polyethylene terephthalate. In particular, when pigmented polyethylene terephthalate is used for the manufacture of films to be used as supports for photographic film, a haze in such supports due to insufficient dispersion of the coloring material and/or the presence of granular foreign material must be completely avoided in order to satisfy the demand for high clarity and optical purity in such materials. As is well known to those skilled in the art, it is necessary that polyethylene terephthalate films manufactured in a melt extrusion process be stretched and heat treated under appropriate conditions in order to gain useful properties. Such stretching very often causes, even if the coloring material is uniformly dispersed in an amorphous unoriented film to such a degree as not to impair the clarity of the film, the formation of cleavages between the undeformable particles of the coloring material and the plastically deformable polyethylene terephthalate matrix. Such cleavages causes a scattering of light, thus, increasing the haze level of the film. Therefore, especially in the manufacture of photographic films, it is necessary to disperse the coloring material into very fine particles, or to dissolve it into a state of molecular dispersion, so as to prevent formation of such cleavages during stretching.
Referring now to the coloring or pigmentation appropriate to radiographic films, methods of indication and determination of color are provided in the Japanese Industrial Standard (JIS) Z8701-1958 and in (JIS) Z8722-1959, respectively.
With regard to the specific prior art, there may be mentioned Swiss Pat. No. 405,227, U.S. Pat. No. 3,215,710 and U.S. Pat. No. 3,488,195.
The Swiss Patent noted above relates to a process for dyeing and printing polyester fibers, especially polyethylene, terephthalate fibers by employing dye-, tri-, and tetra-nitro derivative dyes obtained through the nitrification of diarylamino anthraquinones having the following formula: ##SPC1##
Wherein one of Y is --NH--Aryl and the other two Y's are hydrogen atoms.
With regard to U.S. Pat. No. 3,215,710, this patent discloses a process for preparing 1-hydroxy-4-phenylaminoanthraquinones which are useful for dyeing polyester fibers. These compounds may be structurally illustrated as follows: ##SPC2##
wherein Y.sub.1 and Y.sub.2 are hydrogen or hydroxy; Z.sub.1 and Z.sub.2 are hydrogen or chlorine; A is a lower alkyl group or a lower alkoxyl group; E is chlorine, a lower alkyl group, or a lower alkoxyl group; and n is integer ranging from 0 to 2, both members of one of the pairs of Y.sub.1 and Y.sub.2 and Z.sub.1 and Z.sub.2 being hydrogen atoms.
The phenyl group of the present invention has only one substituent thereon, while that of the above metnioned patent requires at least two substituents. This difference in the substituents on the phenyl group results in a difference in color with respect to the dyes encompassed within each of the generic formulas. The reason for this color difference, results from the fact that the dyes of the aforementioned patent maintain a short wavelength (below 593 m..mu..), while the dyes of the present invention exhibit a wavelength at around 625 m..mu.. and upwards.
As a result of the above fact, both the dyes of U.S. Pat. No. 3,215,710 and Swiss Pat. No. 405,227 exhibit extremely poor heat resistance, which allows these dyes to dramatically change in color during the presence of heat. Consequently, these dyes are not suitable for purposes of the present invention.
The closest prior art known by applicants is U.S. Pat. No. 3,488,195 which discloses a light-sensitive photographic element capable of being employed for radiographic purposes, comprising a linear polyester support containing as a coloring material, at least one of the compound, 1,4-dimesidinoanthraquinone, 1,5-bis(para toluidine)-4,8-dihydroxyanthraquinone, 4-anilino-1,8-dihydroxy-5-nitro-anthraquinone, 5-anilino-4-amino-1,8-dihydroxyanthraquinone, 1,4-bis(2,6-diethylanilino) anthraquinone, 4-(4-beta-hydroxyethylanilino)-1,8-dihydroxy-5-nitroanthraquinone, 4-(4-beta-hydroxyethylanilino)-1,8-dihydroxy-5-aminoanthraquinone, and 1,5-di[p-(beta-hydroxyethoxyethoxyethoxy) phenol] amino-4,8-dihydroxyanthraquinone, and a photographic emulsion layer adhere to at least one surface of said support.
These dyes maybe structurally illustrated as follows:
I. 1,4-dimesidino-anthraquinone ##SPC3## PA0 Ii. 1,5-bis(p-toluidine)-4,8-dihydroxy-anthraquinone ##SPC4## PA0 Iii. 4-anilino-1,8-dihydroxy-5-nitro-anthraquinone ##SPC5## PA0 Iv. 5-anilino-4-amino-1,8-dihydroxy-anthraquinone ##SPC6## PA0 V. 1,4-bis(2,6-diethylanilino)anthraquinone ##SPC7## PA0 Vi. 4-(4-.beta.-hydroxyethylanilino)-1,8-dihydroxy-5-nitro-anthraquinone ##SPC8## PA0 Vii. 4-(4-.beta.-hydroxyethylanilino)-1,8-dihydroxy-5-amino-anthraquinone ##SPC9## PA0 Viii. 1,5-di[p-(.beta.-hydroxyethyoxyethyoxyethyoxy)phenyl]-amino-4,8-dihydroxy- anthraquinone ##SPC10##
As will be seen later on, in the body of this specification, when the dyes of Hunter were compared with the dyes of the present invention for heat resistance, the dyes of the present invention substantially out performed those of Hunter.